Following surgery, medulloblastoma is usually treated with radiation therapy. It is an important “next-step” because microscopic tumor cells can remain in the surrounding brain tissue even after surgery has successfully removed the entire visible tumor. Since these remaining cells can lead to tumor regrowth, the goal of radiation therapy is to reduce the number of left-over cells. Doctors consider several factors in planning radiation therapy: The age of the patient, the location of the tumor, the amount of remaining tumor, and any tumor spread. Since radiating the brain and central nervous system can be damaging to a developing brain, it is usually delayed in children under age 3. Initial treatment for these young children includes surgery followed by chemotherapy to control the tumor. Radiation may be delivered later, if needed.
For older children and adults, conventional external beam radiation therapy is given to the brain and spine. This area is called the craniospinal axis. This form of radiation is given 5 days a week for 5 to 6 weeks. A “boost” is given to the posterior fossa, the region most at-risk because it housed the original tumor. An additional boost may be given to areas of tumor spread. Age and risk factors determine the total doses of radiation given to each area.
While radiation therapy has proven effective, scientists are still looking for new ways to lower the potential side effects of this treatment. Techniques such as focused radiation, also called stereotactic radiosurgery, aims converged beams of radiation at the tumor. Conformal radiation allows doctors to shape the radiation beams to match the tumor’s contour. The goal of these focused forms of radiation is to spare normal brain tissue while treating tumor. Your radiation oncologist, a doctor specially trained in the use of radiation therapy, can talk with you about the best method of radiating you/your child’s tumor.